This invention relates to production and harvesting of novel olefin polymers, both homopolymers and copolymers (or "interpolymers" as they are sometimes referred)
It is well known that crystalline polyolefins generally have isotactic or syndiotactic structures and that amorphous polyolefins generally have considerable atactic structure. U.S. Pat. Nos. 3,112,300 and 3,112,301, for example, describe isotactic polypropylene and provide structural formulae for isotactic and syndiotactic polypropylene. Conventional polymers of this type typically have a crystallinity, or heat of fusion, of 75 Joules per gram (J/g) or higher, and more typically 90 J/g or higher.
In order to produce polyolefins, an olefinic monomer raw material is generally contacted with a suitable catalyst under conditions of pressure and temperature sufficient for causing a polymerization of the monomer. Great volumes of investigation in the field of polymerization catalysis have yielded a multitude of polymeric products having a wide range of physical and chemical properties. By modifications to the catalyst and reaction conditions it is possible in some instances to produce materials especially suitable for a particular application.
Of the various known catalysts used for polymerizing olefins, the prior art patents forthwith presented disclose one type of catalyst used in the formation of such polymers. They include generally a pro-catalyst that is typically formed from the reaction product of a magnesium alkoxide compound of the formula MgR.sub.1 R.sub.2 where R.sub.1 is an alkoxy or aryl oxide group and R.sub.2 is an alkoxide or an aryl oxide group or halogen, and a tetravalent titanium halide wherein the reaction takes place in the presence of an electron donor and, preferably, a halogenated hydrocarbon. These include: U.S. Pat. Nos. 5,118,768; 5,164,352; 5,089,573; 5,118,649; 5,118,767; 5,294,581; 5,118,768; 5,164,352; 5,438,110; 4,990,479; 5,218,052; 5,182,245; 5,153,158; 4,990,477; 3,175,199 3,112,300; 3,112,301 and in European Patent 475,307. These types of catalysts are generally referred to in the art as "Ziegler/Natta" catalysts, named after their pioneering discoverers. These patent specifications in their entirety are herein incorporated by reference.
Another type of catalysts for olefin polymerization known as "metallocenes" have come into widespread usage in recent years. Generally speaking, metallocene catalysts comprise a transition metal atom, typically ziroconium, hafnium, vanadium, or titanium which has at least one cyclopentadienyl ligand pi-bonded to it. Often the transition metal atom is positioned between two cyclopentadienyl ligands wherein the metal atom is said to be "sandwiched" between the two ligands. The famous compound known as ferrocene, discovered by Wilkinson is exemplary of such an arrangement.
In the field of olefin polymerization catalysis, much creative work has been undertaken with regard to modification of the basic structure of ferrocene. Replacement of the iron atom by one of the aforesaid transition metals has provided a basic framework for investigators to modify with the hopes of producing polymers having hitherto unbeknownst beneficial physical properties. By substituting various organic and inorganic moieties in the position of the hydrogen atoms of the basic framework, a multitude of compounds useful in olefin polymerization have been discovered, with nearly each having its own unique effect on polymers produced using it as a catalyst. Examples of patents which have been generated as a result of these types of modifications to the basic framework inlclude: 5,594,080; 4,769,510; 4,808,561; 4,871,705; 4,935,397; 5,578,690; 5,132,262; 5,208,357; 5,232,993; 5,280,074; 5,314,973; 5,322,902; 5,349,100; 5,496,781; 5,525,690; 5,585,508; 5,631,202; 5,637,744; 5,329,033; 5,243,001; 5,241,025; 5,278,264; 5,227,440; 5,214,173; 5,162,466; 5,145,819; 5,120,867; 5,103,030; 5,084,534; 5,064,802; 5,057,475; 5,055,438; 5,017,714; 5,008,228; 4,937,299; 5,081,322; and 5,036,034, the entire contents of which are herein incorporated by reference.
A difficulty is often encountered in the prior art when using either the Ziegler/Natta or metallocene type in that the polymeric materials produced as a result of the polymerization process under particular conditions are often too gummy or sticky to be processed by known means for handling the polymers by conventional means normally employed in processing conventional polypropylene. The polymers are generally classifiable as flexible polyolefins (FPO's). They have less than about 70 Joules per gram of crystallinity. FPO's may be either homopolymers or copolymers.
The limitations of the processing equipment available places a restriction on the type of polymers which can be produced in quantities sufficient for meaningful injection into the stream of commerce. The processibility of the resulting polymers is thus a critical consideration in the design of experiments by researchers who undertake novel catalyst design. A great many potential products are overlooked or ignored simply because there exists no sufficient technology for processing potentially novel polymers. This has left a wide void in materials available in the marketplace, materials which, if produced would have a significant impact on the face of the various polymer industries. Many of the prior art catalysts are capable of producing unique materials, the physical properties of which would provide fertile new uses in various applications. The only problem is that researchers are reluctant to even make attempts at producing the materials, given the knowledge they have concerning the non-processibility of the materials. Thus, although the number of catalysts available is great, the number of polymers having uniquely advantageous physical properties produced therefrom is artificially hindered.
Of particular interest are the catalyst materials described in the U.S. Pat. No. 5,594,080 to Waymouth et al. Although the Waymouth patent discloses the use of ethylene as a comonomer, it is appreciated by those skilled in the art that the use of comonomers other than ethylene results in polymers having even greater stickiness. For a given percentage of comonomer in the feed materials, the stickiness and unprocessability of the polymeric products is seen to increase in direct proportion to the comonomer chain length. It is an object of this invention to permit progress in efforts to bringing to market polymeric materials having physical properties which hindered their ability to be produced in commercial quantities.
Although mention is made of the use of ethylene as a comonomer with propylene in the Waymouth U.S. Pat. No. 5,594,080, no mention is made of the use of other comonomers. This is due to the fact that the stickiness or gumminess which these materials would be likely to possess would render them impossible to produce and process on a large scale. The present invention provides families of novel copolymers using Waymouth-type catalysts. The polymers of this invention are produced using various comonomers in conjunction with propylene including all alpha olefins having between about 1 and 12 carbon atoms per molecule and also styrene and its derivatives.
With regard to processing, amorphous poly alphaolefins including but not limited to amorphous propylene homo and copolymers, are conventionally mixed with water after their production in a reactor to deactivate the catalysts and remove unreacted monomer(s). Removing the catalysts and monomer(s) renders wet, tenaciously sticky, granular chunks of the product. For the material to be shaped into various products, the chunks must be dried and then extruded or otherwise shaped. For purposes of this invention the words "polyolefin material" means a polymerization product made by introducing olefinic monomeric raw material(s) into a reactor in the presence of a suitable catalyst under conditions sufficient to cause polymerization of the monomeric material(s). The monomeric materials useful as feedstocks for the production of polyolefin materials according to the instant invention may be any olefin including: styrene, ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene-, 1-octene, 1-nonene, 1-decene, 1-undecene, and 1-dodecene, or mixtures of these monomers in the presence or absence of a chain transfer control agent such as hydrogen.
Extrusion of the material typically involves feeding the dried chunks of the desired polymer from a hopper to the throat or feed section of a screw-type extruder. The polyolefin material is moved through the extruder by screw flights where it is heated and mechanically worked before it is pelletized or otherwise shaped under high pressure. Alternatively, such materials are also shaped by other high temperature methods such as injection molding, roll milling and compression molding. Both lower and higher molecular weight amorphous poly alphaolefins are typically processed as outlined above.
However, existing methods of product transport and recovery require the introduction of water to carry the material through the several stages of recovery from the polymer reactor to the extruder. The extensive use of water by these methods requires that additional storage tanks, delivery and removal lines, and other miscellaneous equipment be used to introduce, maintain, remove and recycle the necessary volume of water. Additionally, existing methods store the material in a chunk form prior to extrusion into useable products, thus requiring additional storage and transport equipment along with the associated maintenance equipment for this intermediate stage of processing. Thus, a need has arisen for a product recovery method and apparatus for recovery of polyolefins, particularly high molecular weight amorphous poly alphaolefins, wherein the use of water during the product recovery is significantly decreased and wherein the intermediate stage of storing and drying the chunk form of the polyolefin is eliminated to enhance production efficiency.
Conventional processing equipment, such as sigma mixers, kneaders or kneader/extruders, are generally known. This conventional equipment is typically used for batch mixing of various materials. High molecular weight amorphous poly alphaolefins exhibit increased tackiness and viscosity, as well as relatively higher softening temperatures, when compared with conventional lower molecular weight poly alphaolefins. The combination of properties of these higher molecular weight polyolefins provide unique processing problems. For example, when using conventional handling and transport technologies at temperatures at which FPO polymers are processed, high molecular weight amorphous poly alphaolefins tend to plug or clog screws, blades, nozzles, fittings, valves, and piping. This is a particularly troublesome problem for autonomous processing of such materials.
There is also a frequent need to measure the amount of material in a vessel, tank, or other processing or storage facility during polymer production. It is typically desired that the inventory of the vessels not exceed the capacity of the available volume, and it is typically also desired that the vessels not become completely empty. These problems can be avoided by measurement of the existing inventory of the vessels to permit more control over the input into and output from the vessels of materials. Each type of vessel, along with various equipment of varying volume inside the vessel, presents a unique challenge in measurement of its inventory.
Conventional inventory measuring means include the following possibilities and attendant problems. One method involves mechanically or electronically weighing the vessels before and after inventory is added, which has the dual problems of poor precision when the vessel weighs much more than the inventory, as well as the requirement that the vessel be movable thereby necessitating use of flexible connections.
Another conventional method for vessels with liquid inventory involves use of a pressure measuring device to determine the hydrostatic pressure in the vessel, but this method is of minimal use when the inventory is a solid or sticky material. Another method involves measuring the increased attenuation of a high energy radiation beam, such as gamma radiation, as it passes through additional mass, but this faces the same precision problems as the weighing method. Another conventional method involves measurement of the surface level by means such as floats, mechanical paddle wheels, electrical probes, ultrasonic transceivers, etc. Each has its own problems, especially when the material may not be evenly distributed throughout the vessel.
None of the conventional methods of measuring the inventory of a vessel are sufficiently accurate for measuring the amount of sticky, high molecular weight amorphous poly alphaolefins of the present invention for the reasons presented above. Thus, there is a need to determine the inventory of such materials in continuous processing equipment to overcome the limitations of conventional weighing technology.
The present invention includes a method for the recovery of a high molecular weight amorphous polyolefin which overcomes the foregoing and other problems associated with the prior art. This method includes the steps of reacting monomers in a reaction zone to form a high molecular weight amorphous polyolefin material; continuously transferring the polyolefin material along with residual catalyst and unreacted monomer(s) as a mixture from the reaction zone to a conditioning zone of known volume; heating the mixture in the conditioning zone to a temperature of at least about 250.degree. F. while kneading the mixture for a time sufficient to form conditioned polyolefin and to remove unreacted monomer(s); determining the volume of the mixture in the conditioning zone; removing the conditioned polyolefin from the conditioning zone; and controlling at least one of the polyolefin material transfer or conditioned polyolefin removal steps to maintain a sufficient volume of the mixture in the conditioning zone to provide a residence time for the polyolefin which is sufficient to enable removal of a substantial portion of the unreacted monomer(s) while avoiding overheating of the polyolefin.
In this method, the measuring step can include introducing into the conditioning zone a portion of a known volume of a fluid which is non-reactive with the mixture and non-condensable at the conditioning zone temperature to produce a detectable pressure change in the conditioning zone; measuring the volume of the fluid portion and gas that occupies the conditioning zone; and determining the volume of the material mixture in the conditioning zone using the measured and known volumes of the conditioning zone. For example, the measured volume can be subtracted from the known volume of the conditioning zone to determine the volume of the blip material mixture therein.
A preferred fluid portion volume measuring step comprises determining the pressure and temperature of any gas in the conditioning zone before introduction of the fluid portion; determining the pressure and temperature of the known fluid volume before introduction into the conditioning zone; determining the pressure and temperature of the fluid portion which is not introduced into the conditioning zone; measuring the pressure and temperature of the fluid portion and gas that occupy the conditioning zone; and calculating the volume of the fluid portion and gas in the conditioning zone from the measured pressures and temperatures. It is also possible to vent the unreacted monomer(s) from the conditioning zone and to recycle the vented unreacted monomer(s) to the reaction zone.
The invention also may include the steps of controlling the transfer of polyolefin material into the conditioning zone to substantially avoid carryover of polyolefin during the venting step and controlling the polyolefin material transfer, heating, and kneading steps to maintain a substantially constant volume of mixture in the conditioning zone. Alternatively, the polyolefin material may be transferred intermittently to the conditioning zone in the form of blips.
Another aspect of the invention relates to an apparatus for the recovery of a high molecular weight amorphous polyolefin. This apparatus generally would include means for receiving polyolefin material; means for continuously transferring polyolef in material along with residual catalyst and unreacted monomer(s) as a mixture into the receiving means; means for venting unreacted monomer(s) from the receiving means; means for heating the mixture in the receiving means to a temperature of at least about 250OF; means for kneading the mixture in the receiving means for a time sufficient to form conditioned polyolefin and to remove unreacted monomer(s) from the mixture; and means for removing the conditioned polyolefin from the receiving means for recovery of same; wherein the receiving means is pressurized.
The apparatus may also include means for controlling the material transfer means and the venting means to substantially avoid carryover of polyolefin material into the venting means, means for determining the volume of mixture to assist in maintaining a desired inventory in the receiving means, or means for controlling at least one of the material transfer or conditioned polyolefin removal steps to maintain a sufficient volume of mixture in the receiving means to provide a residence time for the polyolefin which is sufficient to enable removal of a substantial portion of the unreacted monomers while avoiding overheating of the polyolefin.
Particularly preferred components of the apparatus include a means for continuously transferring polyolefin material where a blipper valve is the means to intermittently transfer polyolefin material, at least one vent line and at least one knockout pot associated with the vent line as the means for venting unreacted monomer, and an exit transport screw as the means for removing the conditioned polyolefin. Any conventional means for heating the mixture can be used, such as a jacket encompassing the receiving means and a heating medium which passes between the jacket and the receiving means.
Advantageously, the means for kneading the mixture includes rotatable sigma blades, such as two sigma blades which rotate oppositely to each other to knead the mixture while forcing polyolefin between the blades toward the conditioned polyolefin recovery means. The kneading means may also include blade members which have hollow cores and the heating means may be a heating medium disposed in the hollow cores of the blades. Advantageously, the receiving means is operated at a pressure of from about 35 to 100 psig.
Another aspect of the invention relates to a method for measuring the inventory of a vessel with a known volume. This method includes the steps of introducing a portion of a known volume of a fluid from a reservoir into the vessel, which fluid is non-reactive and non-condensable at the vessel temperature, to produce a detectable pressure change in the reservoir; measuring the volume of the fluid portion and gas that occupies the vessel; and determining the amount of inventory in the vessel by subtracting the measured volume from the known volume of the vessel. The fluid portion volume measuring step may include determining the pressure and temperature of the gas in the vessel before introduction of the fluid portion; determining the pressure and temperature of the known fluid volume before introduction into the conditioning zone; determining the pressure and temperature of the fluid portion which is not introduced into the vessel; measuring the pressure and temperature of the fluid portion and gas that occupy the vessel; and calculating the volume of the fluid portion and gas in the vessel from the measured pressures and temperatures. In addition, the fluid introduction step could include introducing a fluid which is non-reactive and non- condensable at the vessel temperature into a reservoir; and measuring the volume of the fluid in the reservoir. In this regard, it is useful to temporarily halt change in the quantity of the inventory in the vessel as the measuring fluid is introduced into the vessel. Thereafter, the measuring fluid can be released from the vessel and normal inventory flow through the vessel can be resumed.